FR2703045A1 - Process for the isomerization of carboxylic acids - Google Patents

Abstract

The present invention relates to a process for the isomerization of carboxylic acids, more precisely of branched acids into corresponding linear acids. More specifically, it consists of a process for the isomerization of at least one branched saturated carboxylic acid, by heating, characterized in that the operation is carried out in the presence of an effective amount of an iridium catalyst and of an iodinated or brominated promoter, the promoter / Ir molar ratio being between 0.1 / 1 and 20/1. This process makes it possible in particular to upgrade methyl glutaric and ethyl succinic acids to adipic acid.

Description

PROCESS FOR ISOMERIZING CARBOXYLIC ACIDS
The present invention relates to a process for the isomerization of carboxylic acids, more precisely branched saturated carboxylic acids, into corresponding linear acids.

 The hydroxycarbonylation of pentenoic acids to prepare adipic acid always leads to the formation of greater or lesser amounts of branched diacids as by-products of the reaction.

 The valorization of these branched diacids thus represents, in particular, an important problem to be solved, in the context of an industrial process for the preparation of adipic acid by hydroxycarbonylation of pentenoic acids.

 In EP-A-0 374 687 there is described a process for isomerizing saturated carboxylic acids by heating under a pressure of carbon monoxide in the presence of a rhodium catalyst and an iodinated or brominated promoter.

 The present invention is characterized by the use of iridium, a catalyst different from that previously described for this reaction.

 More specifically, it consists of a method of isomerization by heating, of at least one branched saturated carboxylic acid, characterized in that it operates in the presence of an effective amount of an iridium catalyst and of an iodinated or brominated promoter, the promoter / Ir molar ratio being between 0.1 / 1 and 20/1.

 Of the branched saturated carboxylic acids, the branched diacids are economically the most interesting to valorize, because of the high amounts formed during the hydroxycarbonylation of pentenoic acids for the preparation of adipic acid.

 These are more specifically 2-methyl-glutaric acid, 2-ethyl-succinic acid and their mixtures with each other and / or with other carboxylic acids or lactones formed together with them, such as, for example, adipic acid, pentenoic acids, valeric acid, gamma-valerolactone.

 In the above mixtures, the compounds other than 2-methylglutaric acid and 2-ethylsuccinic acid may represent up to 50% by weight of the total weight of the mixture.

 For the iridium catalyst required in the present process, various sources of iridium are likely to be employed.

As examples of such sources of iridium, mention may be made of
- metallic Ir; 1r02; Ir2 3
- IrCl3; IrCl3, 3H20
- IrBr3; IrBr3, 3H20
- IrI
Ir2 (C0) 4Cl2; Ir2 (C0) 4I2
Ir2 (C0) 8; Ir4 (CO) l2
- Ir (CO) [P (C6H5) 312I;
- Ir (CO) [P (C 6 H 5) 3] 2 Cl;
- Ir [P (C 6 H 5) 3] 3I;
- HIr [P (C6H5) 3] 3 (CO);
- Ir (acac) (C0) 2
- [IrCl (cod)] 2
(acac = acetylacetonate, cod = 1,5-cyclooctadiene).

 Iridium catalysts which are more particularly suitable are: [IrCl (cod) 2, Ir 4 (CO) 12 and Ir (acac) (CO) 2.

 The amount of catalyst to be used can vary within wide limits.

 In general, a quantity, expressed in moles of iridium metal per liter of reaction mixture, of between 10-4 and 10-1 gives satisfactory results. Lower amounts can be used, but it is observed, however, that the reaction rate is low. Higher quantities have only economic disadvantages.

 Preferably, the concentration of iridium in the reaction mixture is between 5.10-4 and 5.10-2 mol / liter.

 By iodinated or brominated promoter is meant in the context of the process hydrogen iodide, hydrogen bromide and organo-iodine and organo-brominated compounds capable of generating hydrogen iodide and bromide respectively. hydrogen under the reaction conditions; these organo-iodinated and organo-brominated compounds are more particularly the iodides and alkyl bromides having from 1 to 10 carbon atoms, of which methyl iodide and methyl bromide are preferred.

 The promoter / Ir molar ratio is preferably between 1/1 and 10/1.

 The reaction is conducted in the liquid phase. The temperature at which the operation is carried out is generally from 1200 ° C. to 300 ° C. and preferably from 1500 ° C. to 250 ° C.

 Although it is possible to perform the isomerization according to the process of the invention in the absence of carbon monoxide, it is preferable to operate in its presence.

 The total pressure at the reaction temperature can then vary within wide limits. The carbon monoxide partial pressure, measured at 25 ° C., is generally from 0.5 bar to 100 bar and preferably from 1 bar to 80 bar.

 The carbon monoxide used may be substantially pure carbon monoxide or technical grade carbon monoxide as it is commercially available.

 The isomerization reaction of the branched saturated carboxylic acids is conducted either in the acid itself as a liquid medium of the reaction, or in a third solvent.

 As a third solvent, it is possible to use in particular aliphatic carboxylic acids, saturated or unsaturated, or aromatic, having at most 20 carbon atoms, insofar as they are liquid under the reaction conditions. By way of examples of such carboxylic acids, mention may be made of acetic acid, propionic acid, butanoic acid, valeric acid, adipic acid, pentenoic acids, benzoic acid and acid. phenylacetic.

 Other families of solvents may also be used, in particular saturated aliphatic or cycloaliphatic hydrocarbons and their chlorinated derivatives, insofar as they are liquid under the reaction conditions. As examples of such solvents, mention may be made of benzene, toluene, chlorobenzene, dichloromethane, hexane and cyclohexane.

 Solvent mixtures can be used.

 When present in the reaction mixture, the solvent is, for example, from 10% to 99% by volume based on the total volume of said reaction mixture and preferably from 30% to 90% by volume.

 Water is most often present in the reaction mixture.

Generally, it represents from 0 to 20% by weight of the reaction mixture and preferably from 0 to 10%
When the isomerization reaction is carried out in a solvent, an interesting variant consists in operating in a water / solvent mixture that is miscible with water, such as, for example, water / acetic acid.

In such a case, the values of the proportions of the water / water-miscible solvent mixture in the reaction mixture are those indicated previously for the sole solvent.

 The isomerization process according to the invention makes it possible, in particular, to valorize branched saturated dicarboxylic acids obtained in greater or lesser amounts during the hydroxycarbonylation of pentenoic acids. This allows an increase in the overall yield of a process for preparing adipic acid from butadiene via pentenoic acids, adipic acid being one of the raw materials of the preparation of polyamides 6-6.

 The final reaction mixture is treated according to the standard methods used in chemistry, in order to separate the various compounds formed and unreacted branched saturated acids, the latter being able to undergo a new isomerization.

 The process according to the invention can be carried out continuously or discontinuously. When operating continuously, the relative ratios of the reagents, catalyst, promoter and solvent can be set at an optimum value by those skilled in the art, whereas generally in a batch process, these different ratios evolve in function of the progressive transformation of reagents.

 The following examples illustrate the invention.

EXAMPLE 1

In a 125 cm3 autoclave, previously purged with argon, one introduces successively
- [IrCl (cod)] 2: 0.84 mmol
- hydrogen iodide (in aqueous solution
to 57% by weight): 1.2 mmol
2-methyl-glutaric acid: 39 mmol
- acetic acid: 40 cm3
The autoclave is closed, placed in a stirred oven and connected to the CO feed under pressure. 5 bar of CO is set at 25 ° C and then heated to 230 ° C. The pressure is adjusted to 25 bar with CO (corresponding to 17 bar CO partial pressure measured at 25 ° C) and this pressure is maintained for 5 hours at 230 ° C.

 The autoclave is then cooled, then degassed and the reaction mixture is analyzed by gas chromatography (GC) and high performance liquid chromatography (HPLC).

We obtain the following results
- conversion rate (TT) of the acid
2-methylglutaric: 18%
- molar yield (RT) of adipic acid by
compared to processed methylglutaric acid: 37%
- RT to 2-ethylsuccinic acid: 6
- gamma-valerolactone RT: 6 X
- RT in 3-pentenoic acid: 10%
- 2-methyl-butanoic acid RT: 26%
- RT in valeric acid: 16%
EXAMPLE 2

 Example 1 is repeated under the same conditions and with the same amounts of the same reagents, but using 2.5 mmol of hydrogen iodide and 0.42 mmol of [IrCl (cod)] 2.

We obtain the following results
TT of 2-methyl-glutaric acid: 36%
RT adipic acid: 28%
EXAMPLE 3

 Example 1 is repeated under the same conditions and with the same amounts of the same reagents, but using 2.5 mmol of hydrogen iodide and operating at 200 ° C.

We obtain the following results
TT of 2-methyl-glutaric acid: 13%
RT in adipic acid: 30%
EXAMPLE 4

 Example 3 is repeated under the same conditions and with the same amounts of the same reagents, but without connecting the autoclave to the carbon monoxide feed.

We obtain the following results
TT of 2-methyl-glutaric acid: 60%
RT adipic acid: 11%
It is noted that a very large quantity of monoacids containing 5 carbon atoms (valeric acid and methyl-butanoic acid in particular) is obtained.

EXAMPLE 5

In a 50 cm3 glass ampoule, previously purged with argon, is introduced successively
- [IrCl (cod)] 2: 0.21 mmol
- hydrogen iodide (in aqueous solution
to 57% by weight): 0.54 mmol
2-methyl-glutaric acid: 78 mmol
The glass ampoule is placed in a 125 cm3 autoclave, previously purged with argon. The autoclave is closed, placed in a stirred oven and connected to the CO feed under pressure. We put 5 bar of
CO at 25 ° C, then heat to 230 ° C. The pressure is adjusted to 100 bar with CO (corresponding to 59 bar CO partial pressure measured at 25 ° C) and this pressure is maintained for 2 hours at 230 ° C.

 The autoclave is then cooled, degassed and the reaction mixture is analyzed by GC and HPLC.

We obtain the following results
TT of 2-methylglutaric acid: 20%
RT in adipic acid: 37%
EXAMPLE 6

Example 5 is repeated, under the same conditions and with the same amounts of the same reagents, but operating under a pressure of
CO 25 bar at 230 ° C instead of 100 bar.

We obtain the following results
TT of 2-methyl-glutaric acid: 39%
RT adipic acid: 35%
EXAMPLE 7

Example 5 is repeated, under the same conditions and with the same amounts of the same reagents, but operating under a pressure of
CO from 25 bar to 230 ° C instead of 100 bar and allowing to react for 30 minutes in temperature instead of 2 hours.

We obtain the following results
TT of 2-methyl-glutaric acid: 9%
RT adipic acid: 52%
EXAMPLE 8

Example 5 is repeated, under the same conditions and with the same amounts of the same reagents, but operating under a pressure of
CO from 10 bar to 230 ° C instead of 100 bar.

We obtain the following results
TT of 2-methyl-glutaric acid: 62%
RT adipic acid: 20%
EXAMPLE 9

 Example 5 is repeated under the same conditions and with the same amounts of the same reagents, but operating at a temperature of 200 ° C. instead of 230 ° C.

We obtain the following results
TT of 2-methyl-glutaric acid: 3%
RT adipic acid: 64%
EXAMPLE 10

 Example 6 is repeated under the same conditions and with the same amounts of the same reagents, but operating at a temperature of 200 ° C. instead of 230 ° C.

We obtain the following results
TT of 2-methyl-glutaric acid: 5%
RT adipic acid: 73%
EXAMPLE 11

 Example 8 is repeated under the same conditions and with the same amounts of the same reagents, but operating at a temperature of 200 ° C. instead of 230 ° C.

We obtain the following results
TT of 2-methyl-glutaric acid: 6%
RT adipic acid: 83%
EXAMPLE 12

 Example 6 is repeated under the same conditions and with the same amounts of the same reagents, but additionally loading 7.25 mmol of water initially.

We obtain the following results
TT of 2-methylglutaric acid: 15%
RT in adipic acid: 41%
EXAMPLE 13

 Example 5 is repeated under the same conditions and with the same amounts of the same reagents, but replacing HI with 0.54 mmol of HBr at 47% by weight in water.

We obtain the following results
TT of 2-methyl-glutaric acid: 7 X-
RT adipic acid: 53%
EXAMPLE 14

 Example 6 is repeated under the same conditions and with the same amounts of the same reagents, but replacing HI with 0.54 mmol of HBr at 47% by weight in water.

We obtain the following results
TT of 2-methyl-glutaric acid: 17%
RT adipic acid: 25%
EXAMPLE 15

 Example 8 is repeated, under the same conditions and with the same amounts of the same reagents, but replacing HI with 0.54 mmol of HBr at 47% by weight in water.

We obtain the following results
TT of 2-methyl-glutaric acid: 24%
RT in adipic acid: 18%
EXAMPLE 16

In a 50 cm3 glass ampoule, previously purged with argon, is introduced successively
- [IrCl (cod)] 2: 0.21 mmol
- hydrogen iodide (in aqueous solution
to 57% by weight): 0.30 mmol
2-ethylsuccinic acid: 10 mmol
- acetic acid: 10 cm3
The procedure is as in Example 5, with a pressure of CO at a temperature of 25 bar and maintaining the test at 230 ° C. for 5 hours.

We obtain the following results
TT of 2-ethylsuccinic acid: 26%
RT in adipic acid: 47%
RT to 2-methyl-glutaric acid: 19%

Claims (14)

 1) Process for the isomerization by heating, of at least one branched saturated carboxylic acid, characterized in that one operates in the presence of an effective amount of an iridium catalyst and an iodinated or brominated promoter , the promoter / Ir molar ratio being between 0.1 / 1 and 20/1.  2) Process according to claim 1, characterized in that the branched saturated carboxylic acid used is chosen from 2-methylglutaric acid, 2-ethylsuccinic acid and their mixtures with each other and / or with other carboxylic acids or lactones formed at the same time as them, such as adipic acid, pentenoic acids, valeric acid, gamma-valerolactone.  3) Process according to claim 2, characterized in that in the mixture used, the compounds other than 2-methyl-glutaric acid and 2-ethyl-succinic acid represent up to 50% by weight of the weight total of the mixture.  4) Method according to one of claims 1 to 3, characterized in that the iridium catalyst used is selected from  - metallic Ir; IrO2; In203  - IrCl3; IrCl3, 3H20  - IrBr3; IrBr3, 3H20  - IrI3  Ir2 (CO) 4Cl2; Ir2 (CO) 4I2  Ir2 (CO) 8, Ir4 (CO) 12  - Ir (cO) [p (c6H5) 3] 2I;  - Ir (CO) [P (C 6 H 5) Cl  - Ir [P (C6H5) 3] 3I  - HIr [P (C6H5) 3] 3 (CO)  - Ir (acac) (CO) 2  - [IrCl (cod)] 2  5) Process according to one of claims 1 to 4, characterized in that the amount of catalyst, expressed in moles of iridium metal per liter of reaction mixture, is between 10-4 and 10-1 and preferably is included between 5.10-4 and 10-2 mole / liter.  6) Method according to one of claims 1 to 5, characterized in that the iodinated or brominated promoter is selected from hydrogen iodide, hydrogen bromide and organo-iodine and organo-brominated compounds capable of generating respectively hydrogen iodide and hydrogen bromide under the reaction conditions.  7) Method according to one of claims 1 to 6, characterized in that the promoter / Ir molar ratio is between 1/1 and 10/1.  8) Method according to one of claims 1 to 7, characterized in that the reaction is conducted in the presence of carbon monoxide, under a partial pressure of carbon monoxide, measured at 25 "C, from 0.5 bar to 100 bars and preferably from 1 bar to 80 bar.  9) Method according to one of claims 1 to 8, characterized in that the reaction is conducted in the liquid phase at a temperature of 100 C to 300 "C and preferably 150 C to 250" C.  10) Method according to one of claims 1 to 9, characterized in that the isomerization reaction of the carboxylic acid is conducted in the carboxylic acid itself as a liquid medium of the reaction.  11) Method according to one of claims 1 to 9, characterized in that the isomerization reaction of the branched saturated carboxylic acid is conducted in a third solvent selected from aliphatic carboxylic acids, saturated or unsaturated, or aromatic, comprising at most 20 carbon atoms, saturated aliphatic or cycloaliphatic hydrocarbons and their chlorinated derivatives, which are liquid under the reaction conditions.  12) Process according to claim 11, characterized in that the solvent is from 10% to 99% by volume relative to the total volume of the reaction mixture and preferably from 30% to 90% by volume.  13) Method according to one of claims 1 to 12, characterized in that the reaction is conducted in the presence of water.  14) Method according to one of claims 1 to 13, characterized in that the water is from 0 to 20% by weight of the reaction mixture and preferably from 0 to 10%